The present invention relates to a swash plate type compressor, and more particularly, to materials for a swash plate of a swash plate type compressor.
The swash plate type compressor is well known in the prior art and comprises a cylinder block having a plurality of cylinder bores formed in parallel with a cylinder axis and angularly spaced around the cylinder axis. A plurality of pistons are slidably fitted in the cylinder bores. A cylinder head having a suction chamber and a discharge chamber is mounted on one end of the cylinder block through a valve plate assembly so that each of the cylinder bores is connected to the suction chamber and the discharge chamber through a suction valve and a discharge valve mounted on the valve plate assembly. The cylinder block is also formed with a crank chamber adjacent the cylinder bores at the opposite side of the cylinder head end. In the crank chamber, a driving mechanism including a swash plate is disposed and drives the pistons to reciprocate in the cylinder bores. Reciprocation of the pistons sucks fluid such as refrigerant gas into the cylinder bores through the suction valve from the suction chamber and compresses and discharged the fluid to the discharge chamber through the discharge valve. Thus, fluid compression is carried out.
The driving mechanism comprises a drive shaft which is disposed in the crank chamber to extend on the cylinder axis and which is rotatably supported to the cylinder block. The swash plate is of a circular disk having a center hole and is disposed around the drive shaft which passes through the center hole but is inclined from the drive shaft by a predetermined slant or inclination angle. The swash plate is coupled to the drive shaft with a coupling mechanism and is thereby rotatable together with the drive shaft. Each of the pistons has a piston rod extending into the crank chamber in parallel with the cylinder axis. The piston rod is slidably connected to the outer periphery of the swash plate through sliding shoes. Thus, when the drive shaft rotates, each of the pistons are reciprocatively moved in the direction of the cylinder axis through the piston rod by the swash plate rotating together with the drive shaft.
Typical structures of the swash plate type compressor are disclosed in, for example, EP-A-0 587 023, U.S. Pat. No. 5,382,139, EP-A-0 740 076 and others. These documents disclose a variable capacity type compressor where the inclination angle of the swash plate is variable so as to regulate the displacement of the compressor. That is, when the slant angle is changed, the reciprocating stroke of the piston is also changed. Therefore, the displacement of the compressor is changed.
Although those documents discloses a structure where all of the cylinder bores are disposed at one side of the crank chamber, another structure is also known which is provided with another set of cylinder bores at the opposite side of the crank chamber with another set of pistons reciprocated within the set of cylinder bores by the same swash plate, as disclosed in, for example, JP-A-2 267371.
The swash plate type compressor, which can be provided with various structures as described above, is used for refrigerant compressor in an automotive air-conditioning system. In the application, the automotive engine output is utilized to drive the compressor. In detail, the engine output is selectively coupled with the drive shaft of the compressor through an electromagnetic clutch as is shown in FIG. 1 of EP-A-0 740 076.
In the swash plate type compressor, the swash plate and the sliding shoe are conventionally made of iron alloy. In specifically, the sliding shoe is made of bearing steel because it comes in sliding contact with the swash plate and the piston rod during operation of the compressor. On the other hand, since the outer peripheral portion or the sliding portion of the swash plate is in a sliding contact with the shoe, the surface of the sliding portion is coated with a coat of a copper-based bearing alloy so as to realize smooth sliding contact with the shoe. The copper-based bearing alloy coat is formed by sintering, thermal spraying, cladding, welding, or the like. After forming the coat, the coat is finished to obtain demanded accuracies in thickness and roughness.
However, the use of the copper-based bearing alloy coat on the swash plate makes the production process of the swash plate complicated and causes the cost of the swash plate increased. Further, the swash plate possibly suffers from a problem of peeling or separation at the interface between the iron based alloy and the copper-based bearing alloy.
In an application of the swash plate compressor for automotive air conditioning system using the electromagnetic clutch, the swash plate of the iron-based alloy is easily magnetized by magnetic flux from the electromagnetic clutch so that the compressor particularly has a disadvantage of damage or wear of the surfaces of the swash plate and shoes. This is because the swash plate magnetized attracts any iron powder caused by wear of any iron or iron alloy part or parts of the compressor, and the iron powder readily enters the clearances between the swash plate and the shoes.